* {
    margin: 0;
    padding: 0
}

.left,
.right {
    height: 100vh;
}

.box {
    display: flex;
}

.left {
    width: 200px;
    background: yellow;
    position: relative;
    z-index: 10;
}

.right {
    /* width: 200px; */
    flex: 1;
    background: blue;
    position: relative;
    z-index: 5
}